Anatomical step-by-step dissection of common approaches to the third ventricle for trainees: surgical anatomy of the anterior transcortical and interhemispheric transcallosal approaches, surgical principles, and illustrative pediatric cases.

PURPOSE: To create a high-quality, cadaver-based, operatively oriented resource documenting the anterior transcortical and interhemispheric transcallosal approaches as corridors to the third ventricle targeted towards neurosurgical trainees at all levels. METHODS: Two formalin-fixed, latex-injected specimens were dissected under microscopic magnification and endoscopic-assisted visualization. Dissections of the transcortical and transcallosal craniotomies with transforaminal, transchoroidal, and interforniceal transventricular approaches were performed. The dissections were documented in a stepwise fashion using three-dimensional photographic image acquisition techniques and supplemented with representative cases to highlight pertinent surgical principles. RESULTS: The anterior transcortical and interhemispheric corridors afford excellent access to the anterior two-thirds of the third ventricle with varying risks associated with frontal lobe versus corpus callosum disruption, respectively. The transcortical approach offers a more direct, oblique view of the ipsilateral lateral ventricle, whereas the transcallosal approach readily establishes biventricular access through a paramedian corridor. Once inside the lateral ventricle, intraventricular angled endoscopy further enhances access to the extreme poles of the third ventricle from either open transcranial approach. Subsequent selection of either the transforaminal, transchoroidal, or interforniceal routes can be performed through either craniotomy and is ultimately dependent on individual deep venous anatomy, the epicenter of ventricular pathology, and the concomitant presence of hydrocephalus or embryologic cava. Key steps described include positioning and skin incision; scalp dissection; craniotomy flap elevation; durotomy; transcortical versus interhemispheric dissection with callosotomy; the aforementioned transventricular routes; and their relevant intraventricular landmarks. CONCLUSIONS: Approaches to the ventricular system for maximal safe resection of pediatric brain tumors are challenging to master yet represent foundational cranial surgical techniques. We present a comprehensive operatively oriented guide for neurosurgery residents that combines stepwise open and endoscopic cadaveric dissections with representative case studies to optimize familiarity with third ventricle approaches, mastery of relevant microsurgical anatomy, and preparation for operating room participation.

Longitudinal Reference Values for Cerebral Ventricular Size in Preterm Infants Born at 23-27 Weeks of Gestation.

OBJECTIVE: To establish longitudinal reference values for cerebral ventricular size in the most vulnerable patients at risk for intraventricular hemorrhage (IVH) and posthemorrhagic ventricular dilatation (PHVD). STUDY DESIGN: This retrospective study included neurologically healthy preterm neonates born at 230/7-266/7 weeks of gestational age between September 2011 and April 2019. Patients were treated at 2 Austrian tertiary centers, Medical University of Vienna and Medical University of Innsbruck. All available cerebral ultrasound scans until 30 weeks corrected age were analyzed. Ventricular measurements included ventricular index, anterior horn width (AHW), and thalamo-occipital distance (TOD) and longitudinal percentiles were created. RESULTS: The study cohort consisted of 244 preterm neonates, with a median gestational age of 253/7 weeks (IQR, 244/7-260/7 weeks) and a median birth weight of 735 g (IQR, 644-849 g). A total of 993 ultrasound scans were available for analysis, resulting in >1800 measurements of ventricular index, AHW, and TOD. Special attention was given to the 97th percentile as well as 2 mm and 4 mm above the 97th percentile, which are used internationally as cutoffs for intervention in the presence of PHVD. CONCLUSIONS: We present percentile charts based on a cohort of extremely premature infants including neonates born at the border of viability suited to follow-up the most vulnerable patients at risk for IVH and PHVD. Furthermore, we provide an extensive literature research and comparison of all available reference values, focusing on ventricular index, AHW, and TOD.

Freehand stereotactic ventricular catheter insertion for ventriculoperitoneal shunts based on individualized radio-anatomical landmarks.

INTRODUCTION: The accurate placement of the ventricular catheter (VC) is critical in reducing the incidence of proximal failure of ventriculoperitoneal shunts (VPSs). The standard freehand technique is based on validated external anatomical landmarks but remains associated with a relatively high rate of VC malposition. Already proposed alternative methods have all their specific limitations. Herein, we evaluate the accuracy of our adapted freehand technique based on an individualized radio-anatomical approach. Reproducing the preoperative imaging on the patient's head using common anatomical landmarks allows to define stereotactic VC coordinates to be followed at surgery. MATERIAL AND METHODS: Fifty-five consecutive patients treated with 56 VPS between 11/2005 and 02/2020 fulfilled the inclusion criteria of this retrospective study. Burr hole coordinates, VC trajectory, and length were determined in all cases on preoperative computed tomography (CT) scan and were accurately reported on patients' head. The primary endpoint was to evaluate VC placement accuracy. The secondary endpoint was to evaluate the rate and nature of postoperative VC-related complications. RESULTS: Our new technique was applicable in all patients and no VC-related complications were observed. Postoperative imaging showed VC optimally placed in 85.7% and sub-optimally placed in 14.3% of cases. In all procedures, all the holes on the VC tip were found in the ventricular system. CONCLUSIONS: This simple individualized technique improves the freehand VC placement in VPS surgery, making its accuracy comparable to that of more sophisticated and expensive techniques. Further randomized controlled studies are required to compare our results with those of the other available techniques.

Effects of Spaceflight on Astronaut Brain Structure as Indicated on MRI.

BACKGROUND: There is limited information regarding the effects of spaceflight on the anatomical configuration of the brain and on cerebrospinal fluid (CSF) spaces. METHODS: We used magnetic resonance imaging (MRI) to compare images of 18 astronauts' brains before and after missions of long duration, involving stays on the International Space Station, and of 16 astronauts' brains before and after missions of short duration, involving participation in the Space Shuttle Program. Images were interpreted by readers who were unaware of the flight duration. We also generated paired preflight and postflight MRI cine clips derived from high-resolution, three-dimensional imaging of 12 astronauts after long-duration flights and from 6 astronauts after short-duration flights in order to assess the extent of narrowing of CSF spaces and the displacement of brain structures. We also compared preflight ventricular volumes with postflight ventricular volumes by means of an automated analysis of T1-weighted MRIs. The main prespecified analyses focused on the change in the volume of the central sulcus, the change in the volume of CSF spaces at the vertex, and vertical displacement of the brain. RESULTS: Narrowing of the central sulcus occurred in 17 of 18 astronauts after long-duration flights (mean flight time, 164.8 days) and in 3 of 16 astronauts after short-duration flights (mean flight time, 13.6 days) (P<0.001). Cine clips from a subgroup of astronauts showed an upward shift of the brain after all long-duration flights (12 astronauts) but not after short-duration flights (6 astronauts) and narrowing of CSF spaces at the vertex after all long-duration flights (12 astronauts) and in 1 of 6 astronauts after short-duration flights. Three astronauts in the long-duration group had optic-disk edema, and all 3 had narrowing of the central sulcus. A cine clip was available for 1 of these 3 astronauts, and the cine clip showed upward shift of the brain. CONCLUSIONS: Narrowing of the central sulcus, upward shift of the brain, and narrowing of CSF spaces at the vertex occurred frequently and predominantly in astronauts after long-duration flights. Further investigation, including repeated postflight imaging conducted after some time on Earth, is required to determine the duration and clinical significance of these changes. (Funded by the National Aeronautics and Space Administration.).

Handedness related differences in the intracranial fluid spaces in healthy adults.

Purpose: Our study aimed to determine the possible differences in linear measurements and linear indices values of intracranial fluid spaces (IFS) between right- and left-handed adults.Methods: This work has been carried out on 148 subjects (72 men and 76 women). In the study, 88 right-handers and 60 left-handers were included. Forty of the right-handers were male, 48 were female, and 32 of the left-handers were male, and 28 were female. The ages were between 20 and 50 years. Linear measurements were obtained based on magnetic resonance imaging (MRI) studies. A 1.5-T MRI scanner was used to obtain axial images. The ten parameters were estimated from MRI scans.Results: There was no correlation between parameters and age. In our study, interestingly, as can be seen from the tables, most of the parameters with statistically significant differences were higher in favour of left-handed subjects. In most of the linear measurement results, IFS values of the right hemisphere in right-handers, and the left hemisphere in left-handers were higher. Similar results were found in favour of the left-handed in most of the linear ventricular indices.Conclusion: Linear measurements and linear indices values of IFS were mostly higher in left-handers than in right-handed individuals.

A critical appraisal of Monro's erroneous description of the cerebral interventricular foramina: Age-related magnetic resonance imaging spatial morphometry and a proposed new terminology.

Anatomic connections between the cerebral lateral and third ventricles have been mischaracterized since Monro's original erroneous description of his eponymous foramina (FoMs) as being only one T-shaped passage. Accurate knowledge of the in vivo three-dimensional (3D) configuration of FoM has important clinical neuroendoscopic, neurosurgical, and neuroimaging implications. We retrospectively analyzed volumetric high-resolution brain magnetic resonance imaging of 100 normal individuals to characterize the normal spatial anatomy and morphometry for each FoM. We measured the true anatomical 3D angulations of FoMs relative to standard neuroimaging orthogonal planes, and their minimum width, depth, and distance between the medial borders of bilateral FoMs. The right and left FoMs were separate, distinct, and in a V-shaped configuration. Each FoM was a round, oval, or crescent-shaped canal-like passage with well-defined borders formed by the semicircular concavity of the ipsilateral forniceal column. The plane of FoM was angled on average 56.8° ± 9.1° superiorly from the axial plane, 22.5° ± 10.7° laterally, and 37.0° ± 6.9° anteriorly from the midsagittal plane; all these angles changing significantly with increasing age. The mean narrowest diameter of FoM was 2.8 ± 1.2 mm, and its depth was 2.5 ± 0.2 mm. Thus, the true size and orientation of FoM differs from that depicted on standard neuroimaging. Notably, in young subjects, FoM has a diameter smaller than its depth, a configuration akin to a short, small canal. We propose that the eponym "Monro" no longer be associated with this structure, and the term "foramen" be abandoned. Instead, FoM should be more appropriately renamed as the "interventricular canaliculus," or IVC, for short.

From the wax cast of brain ventricles (1508-9) by Leonardo da Vinci to air cast ventriculography (1918) by Walter E. Dandy.

The mold of the human cerebral ventricles produced in 1918 by Walter E. Dandy had an experimental precedent, a wax cast of ox ventricles made four hundred years earlier (1508-9) by Leonardo da Vinci (1452-1519). This paper is an homage to the epitome of Renaissance and polymath Leonard da Vinci, as well as to Walter Edward Dandy (1886-1946) who developed the ventriculography (1918) and pneumoencephalography (1919) techniques. Pneumoencephalography was applied broadly up to the late 1970s, when it was replaced by less invasive and more accurate neuroimaging techniques.

The hippocampal-to-ventricle ratio (HVR): Presentation of a manual segmentation protocol and preliminary evidence.

Disentangling age-related changes from developmental variations in hippocampal volume has proven challenging. This article presents a manual segmentation protocol for the hippocampal-to-ventricle ratio (HVR), a measure combining the assessment of hippocampal volume with surrounding ventricular volume. By providing in a single measure both a standard volumetric assessment of the hippocampus and an approximation of volume loss, based on ventricular enlargement, we believe the HVR provides a superior cross-sectional estimation of hippocampal structural integrity. In a first attempt to validate this measure, we contrasted the HVR and standard hippocampal volume in their associations with age and memory performance in two independent cohorts of healthy aging individuals. The first cohort consisted in 50 cognitively normal subjects (mean age: 66.8 years, SD: 4.96, range: 60-75 years), while the second cohort included 88 cognitively normal subjects (mean age: 65.06 years, SD: 6.42, range: 55-80 years). We showed that the manual segmentation protocol for the HVR can be implemented with high reliability. In both cohorts, the HVR showed stronger negative associations with age than standard hippocampal volume. Correlations with memory performance were also numerically superior with the HVR than standard hippocampal volume, across the two cohorts. These findings support an added benefit of using the HVR over standard hippocampal volume when examining relationships with age or memory function in aging individuals. Although further validation is required, we propose that the computation of the HVR is a promising method to improve the evaluation of hippocampal integrity from cross-sectional MR images.

Molecular anatomy and functions of the choroidal blood-cerebrospinal fluid barrier in health and disease.

The barrier between the blood and the ventricular cerebrospinal fluid (CSF) is located at the choroid plexuses. At the interface between two circulating fluids, these richly vascularized veil-like structures display a peculiar morphology explained by their developmental origin, and fulfill several functions essential for CNS homeostasis. They form a neuroprotective barrier preventing the accumulation of noxious compounds into the CSF and brain, and secrete CSF, which participates in the maintenance of a stable CNS internal environment. The CSF circulation plays an important role in volume transmission within the developing and adult brain, and CSF compartments are key to the immune surveillance of the CNS. In these contexts, the choroid plexuses are an important source of biologically active molecules involved in brain development, stem cell proliferation and differentiation, and brain repair. By sensing both physiological changes in brain homeostasis and peripheral or central insults such as inflammation, they also act as sentinels for the CNS. Finally, their role in the control of immune cell traffic between the blood and the CSF confers on the choroid plexuses a function in neuroimmune regulation and implicates them in neuroinflammation. The choroid plexuses, therefore, deserve more attention while investigating the pathophysiology of CNS diseases and related comorbidities.

Three-dimensional ultrasound cranial imaging and early neurodevelopment in preterm growth-restricted infants.

AIM: Fetal growth restriction (FGR) is associated with increased perinatal morbidity, mortality and long-term neurodevelopmental sequelae. The objective of this study was to examine whether information about early neurodevelopmental deficits was evident using three-dimensional head ultrasound and developmental assessments in preterm infants with FGR, compared with appropriate for gestational age (AGA) infants in the early post-natal period. METHODS: Twenty preterm FGR infants weighing <10th centile and born between 28 and 32 weeks were compared with age-matched AGA infants. In the second post-natal week after birth, we used three-dimensional ultrasound to assess cerebral ventricular volumes. Prechtl General Movement Assessments were performed at 4-6 weeks after birth. Test of Infant Motor Performance (TIMP) to measure functional motor behaviour was performed at 4-6 and 12-14 weeks corrected age. RESULTS: There was no statistically significant difference in the combined cerebral ventricular volume between the two groups (FGR, 0.81 ± 0.42 vs. AGA 0.72 ± 0.38 cm3 , P = 0.4). The TIMP assessment at 12-14 week term corrected demonstrated lower scores (worse performance) in FGR infants compared with the AGA cohort (regression coefficient: -7.74 (95% CI -16.06, 0.57); P = 0.07). We observed a significant correlation between greater ventricular volume and lower TIMP scores in the cohorts separately and also overall (FGR, r = -0.5, P = 0.06 vs. AGA, r = -0.62, P = 0.007 and overall, r = -0.53, P = 0.001). CONCLUSION: Ultrasound in the early weeks may be useful to detect the neuropathology which could then mediate functional consequences.

Tegmento-vermian dysplasia: radiologic features of a novel described anatomic variation.

Here we present the incidental radiological findings of a case that has a huge pontine tegmental cap orienting posteriorly towards the fourth ventricle and continues with the inferior vermis, accompanied by a midline anterior midbrain cleft. Having knowledge about this variation will prevent a misdiagnosis of a posterior fossa tumor and eventual unnecessary biopsy or operation.

Dorsal extensions of the fastigium cerebelli: an anatomical study using magnetic resonance imaging.

BACKGROUND AND PURPOSE: The fastigium cerebelli is an important topographical landmark for neurosurgeons and radiologists. However, few studies have characterized the morphology of the fastigium cerebelli. We aimed to investigate the fastigium cerebelli using postmortem specimens and magnetic resonance imaging (MRI) in vivo. MATERIALS AND METHODS: Three cadaveric brains were midsagittally sectioned for observing the fastigium cerebelli. Additionally, 66 outpatients underwent MRI, including sagittal T1-weighted imaging, axial T2-weighted imaging, and coronal constructive interference in steady-state (CISS) sequence. RESULTS: In the cadaveric specimens, the fastigium cerebelli was observed as a beak-like dorsal protrusion of the fourth ventricle. Its inner surface was observed as a small fovea. On serial CISS images, the fastigium cerebelli consistently possessed a pair of triangular-shaped, dorsal extensions lying parasagittally along the nodule. These extensions were classified as symmetrical, right-side dominant, or left-side dominant. The symmetrical type was the most predominant and comprised 60.6% of the extensions, while the right-side dominant and left-side dominant types comprised 13.6 and 25.8%, respectively. In 91% of the 66 patients, the number of slices covering the entirety of the dorsal extensions were the same on both sides. The fastigial angle (θ) formed by lines tangent to the superior and inferior medullary velums varied widely. CONCLUSIONS: The fastigium cerebelli has a pair of dorsal extensions lying parasagittally along the nodule. Coronal CISS sequence is useful in delineating the fastigium cerebelli in vivo.

Visualization of the cavum septi pellucidi, cavum Vergae, and cavum veli interpositi using magnetic resonance imaging.

PURPOSE: The morphology of the cavum septi pellucidi (CSP), cavum Vergae (CV), and cavum veli interpositi (CVI) has been infrequently explored with neuroimaging. The aim of the present study was to delineate these cavities using magnetic resonance (MR) imaging. METHODS: A total of 71 patients were enrolled in the present study. Following initial examinations with conventional MR sequences, constructive interference in steady-state (CISS) sequence was performed in the coronal and sagittal sections for 60 and 11 patients, respectively. RESULTS: The coronal CISS images at the level of the aqueduct showed two distinct morphologies of the CV roof, one formed by the fornices with varying degrees of conjugation and the other formed by the corpus callosum with completely separated fornices. Appearance of the CSP was classified into four distinct types. Furthermore, the CVI presented two distinct appearances. CONCLUSIONS: Typically, the CSP, CV, and CVI present with asymptomatic conditions with morphological variabilities. Visualization of the CSP, CV, and CVI using the CISS sequences may be useful when managing lesions affecting these cavities.

Estimated ventricle size using Evans index: reference values from a population-based sample.

BACKGROUND AND PURPOSE: Evans index is an estimate of ventricular size used in the diagnosis of idiopathic normal-pressure hydrocephalus (iNPH). Values >0.3 are considered pathological and are required by guidelines for the diagnosis of iNPH. However, there are no previous epidemiological studies on Evans index, and normal values in adults are thus not precisely known. We examined a representative sample to obtain reference values and descriptive data on Evans index. METHODS: A population-based sample (n = 1235) of men and women aged ≥70 years was examined. The sample comprised people living in private households and residential care, systematically selected from the Swedish population register. Neuropsychiatric examinations, including head computed tomography, were performed between 1986 and 2000. RESULTS: Evans index ranged from 0.11 to 0.46. The mean value in the total sample was 0.28 (SD, 0.04) and 20.6% (n = 255) had values >0.3. Among men aged ≥80 years, the mean value of Evans index was 0.3 (SD, 0.03). Individuals with dementia had a mean value of Evans index of 0.31 (SD, 0.05) and those with radiological signs of iNPH had a mean value of 0.36 (SD, 0.04). CONCLUSIONS: A substantial number of subjects had ventricular enlargement according to current criteria. Clinicians and researchers need to be aware of the range of values among older individuals.

Anatomical subgroup analysis of the MERIDIAN cohort: ventriculomegaly.

OBJECTIVE: To assess the contribution of fetal magnetic resonance imaging (MRI) in fetuses of the MERIDIAN cohort diagnosed with ventriculomegaly (VM) as the only abnormal intracranial finding on antenatal ultrasound. METHODS: This was a subgroup analysis of the MERIDIAN study of fetuses with only VM diagnosed on ultrasound in women who had a subsequent MRI examination within 2 weeks and for whom outcome reference data were available. The diagnostic accuracy of ultrasound and MRI was reported in relation to the severity of VM. The difference in measurements of trigone size on the two imaging methods and the clinical impact of adding MRI to the diagnostic pathway were also studied. RESULTS: In 306 fetuses with VM, ultrasound failed to detect 31 additional brain abnormalities, having an overall diagnostic accuracy of 89.9% for ultrasound, whilst MRI correctly detected 27 of the additional brain abnormalities, having a diagnostic accuracy of 98.7% (P < 0.0001). There were other brain abnormalities in 14/244 fetuses with mild VM on ultrasound (diagnostic accuracy, 94.3%) and MRI correctly diagnosed 12 of these (diagnostic accuracy, 99.2%; P = 0.0005). There was a close agreement between the size of trigones measured on ultrasound and on MRI, with categorical differences in only 16% of cases, showing that MRI did not systematically overestimate or underestimate trigone size. Complete prognostic data were available in 295/306 fetuses and the prognosis category changed after MRI in 69/295 (23.4%) cases. The overall effect of MRI on clinical management was considered to be 'significant', 'major' or 'decisive' in 76/295 (25.8%) cases. CONCLUSION: Our data suggest that a woman carrying a fetus with VM as the only intracranial finding on ultrasound should be offered an adjuvant investigation by MRI for further evaluation. Copyright © 2017 ISUOG. Published by John Wiley & Sons Ltd.

Linear relationship found by magnetic resonance imaging between cerebrospinal fluid volume and body weight in dogs.

Despite numerous studies on cerebrospinal fluid (CSF) and its importance during hydrocephalus or myelography, no reliable values exist about its overall volume in dogs. In this study, our aim was to measure the intracranial (IC) volume of CSF in dogs and assess its possible relationship with body size and the symmetry of the lateral ventricles. We ran a 3D magnetic resonance imaging (MRI) sequence on the central nervous system of 12 healthy, male mongrel dogs between 3-5 years of age and 7.5-35.0 kg body weight. A validated semiautomatic segmentation protocol was implemented to segment the CSF and measure its volume. Values for the volume of the ventricular compartment were between 0.97 and 2.94 ml, with 62.1 ± 11.7% in the lateral ventricles, 17.6 ± 4.9% in the third ventricle, 4.9 ± 1.6% in the aqueductus mesencephali and 15.5 ± 6.6% in the fourth ventricle. In 11 cases a significant asymmetry was found between the lateral ventricles. The results suggest that it may be normal for a dog to have one of the lateral ventricles 1.5 times larger than the other. The correlation between body weight and CSF volume was linear, indicating that the current dosage protocols for myelography, based on a hypothetical proportional relationship with body weight, may have to be revised.

Hydrocephalus: the role of cerebral aquaporin-4 channels and computational modeling considerations of cerebrospinal fluid.

Aquaporin-4 (AQP4) channels play an important role in brain water homeostasis. Water transport across plasma membranes has a critical role in brain water exchange of the normal and the diseased brain. AQP4 channels are implicated in the pathophysiology of hydrocephalus, a disease of water imbalance that leads to CSF accumulation in the ventricular system. Many molecular aspects of fluid exchange during hydrocephalus have yet to be firmly elucidated, but review of the literature suggests that modulation of AQP4 channel activity is a potentially attractive future pharmaceutical therapy. Drug therapy targeting AQP channels may enable control over water exchange to remove excess CSF through a molecular intervention instead of by mechanical shunting. This article is a review of a vast body of literature on the current understanding of AQP4 channels in relation to hydrocephalus, details regarding molecular aspects of AQP4 channels, possible drug development strategies, and limitations. Advances in medical imaging and computational modeling of CSF dynamics in the setting of hydrocephalus are summarized. Algorithmic developments in computational modeling continue to deepen the understanding of the hydrocephalus disease process and display promising potential benefit as a tool for physicians to evaluate patients with hydrocephalus.

Anatomical configurations associated with posthemorrhagic hydrocephalus among premature infants with intraventricular hemorrhage.

OBJECTIVE Intraventricular hemorrhage (IVH) is a complication of prematurity often associated with ventricular dilation, which may resolve over time or progress to posthemorrhagic hydrocephalus (PHH). This study investigated anatomical factors that could predispose infants with IVH to PHH. METHODS The authors analyzed a cohort of premature infants diagnosed with Grade III or IV IVH between 2004 and 2014. Using existing ultrasound and MR images, the CSF obstruction pattern, skull shape, and brain/skull ratios were determined, comparing children with PHH to those with resolved ventricular dilation (RVD), and comparing both groups to a set of healthy controls. RESULTS Among 110 premature infants with Grade III or IV IVH, 65 (59%) developed PHH. Infants with PHH had more severe ventricular dilation compared with those with RVD, although ranges overlapped. Intraventricular CSF obstruction was observed in 36 (86%) of 42 infants with PHH and 0 (0%) of 18 with RVD (p < 0.001). The distribution of skull shapes in infants with PHH was similar to those with RVD, although markedly different from controls. No significant differences in supratentorial brain/skull ratio were observed; however, the mean infratentorial brain/skull ratio of infants with PHH was 5% greater (more crowded) than controls (p = 0.006), whereas the mean infratentorial brain/skull ratio of infants with RVD was 8% smaller (less crowded) than controls (p = 0.004). CONCLUSIONS Among premature infants with IVH, intraventricular obstruction and infratentorial crowding are strongly associated with PHH, further underscoring the need for brain MRI in surgical planning. Prospective studies are required to determine which factors are cause and which are consequence, and which can be used to predict the need for surgical intervention.